The majority of diapers in use today, both for adults and children are of the disposable type. Over time, disposable diapers have presented improved comfort levels, fluid absorption and dispersion and typically include a layer in contact with the skin that feels dry over extended periods of time. These advances in disposable diapers, at one point rendered conventional cotton or flannel diapers almost obsolete.
A major drawback of disposable diapers is that they are not readily biodegradable and with ever increasing use, this has resulted in an overload at garbage and landfill sites to the point of causing serious environmental problems. Furthermore, disposable diapers or incontinence pads from hospitals are treated as infectious waste and must be disposed of at special landfill sites, thereby adding to the critical storage at such sites.
With the recent increase in public awareness and concern with environmental issues along with a move towards reducing waste, there has been renewed interest in washable and reusable diapers. This interest is however constrained by the performance of reusable and washable diapers when compared with the advances in disposable diapers. To date, disposable diapers and incontinence pads are used in the overwhelming majority of cases as their comfort, dryness and absorption qualities have been superior to those of reusable diapers and incontinence pads. Due to the competitive marketplace and high demands and expectations of users, there is a need in the art for an improved reusable and washable diaper which provides equivalent comfort, dryness and absorption qualities as disposable diapers.
One prior art reusable diaper, disclosed in U.S. Pat. No. 5,267,991 (Dec. 7, 1993) to Gillies et al. (hereinafter, the '991 Patent), attempted to match the performance of disposable diapers with the inclusion of an absorbent mat produced using a viscose rayon fibre developed by Cortaulds Limited and produced under the GALAXY™ and GALAXY I™ brands. The GALAXY I™ fibre, having a trilobal configuration, was found to have a relatively even fluid dispersion characteristic making it ideal for use in reusable diapers. Both the aforementioned fibres exhibited a water imbibition characteristic of from 100-345%.
While the use of viscose rayon fibres in applications requiring high absorption, such as tampons, was known, the '991 Patent disclosed a method for forming the viscose rayon fibres into a washable and reusable mat, thus allowing them to be used in reusable diaper or incontinence pad applications. The method included providing a plurality of non-woven layers of carded and cross-laid viscose rayon fibres having a cross-section of substantially rigid, multi-limbed configuration and stitchbonding said layers into a cohesive web with a thread under medium tension to stabilize and maintain the web such that the fibres that are gripped by the threads are not bunched up and tightened in a manner that would interfere with uniform absorption and dispersion of a fluid being absorbed.
The carding and cross-laying steps are well known in the art of producing fabrics. Cross-laying involves laying the fibres in layers offset by ninety degrees until a desired thickness is reached. With the viscose rayon fibres, this allows for fluid dispersion optimized along each fibre and therefore fluid is drawn substantially along the two axes as they are cross-laid. This dispersion, while far superior to traditional cotton diapers, needs to be improved upon to match the absorption and dispersion characteristics of current disposable diapers. There is thus a need in the art for a reusable and washable diaper which provides improved fluid absorption and dispersion.
The stitchbonding step of the '991 Patent was carried out using a MALLYMO® stitchbonding machine made by Textina Inc. As is well known and common practice in the art, prior to stitchbonding, the fabric or web to be stitchbonded is temporarily bonded or otherwise held cohesively such that the web can be maintained in a given shape and fed easily through the stitchbonding machine. This results in a stitchbonded mat having a substantially controlled shape. Typically, as in the manufacture of felt, such pre-stitchbonding processing steps involve a chemical or thermal bonding; however these preliminary steps were found by the inventor to interfere with the absorbency of the viscose rayon fibres, and were for this reason unsuitable for use in the method of the '991 Patent. The alternative, as carried out when using a MALLYMO® stitchbonding machine is to use a needle punch machine, (which, contrary to the suggestion of its name, uses no thread) prior to feeding the web therethrough for stitchbonding. A needle punch machine causes some fibres to break or to entangle with others, thereby constraining the web for easier feeding through the stitchbonding machine.
It has also been found by the inventor that the needle punch step, while not limiting absorbency to the same degree as chemical or thermal bonding, still results in less than optimal absorbency and fluid dispersion due to breakage and entanglement of the fibres that make up the web. This is so, as it has been found that fluid dispersion is optimized along the length of a given individual fibre. Accordingly, broken web fibres result in the stitchbonded threads not gripping entire fibres, with a resultant loss of directionality of individual fibres within the web. Similarly, entangled fibres lose the original directionality with which they were laid within the web. Both effects combine to cause reduced fluid dispersion through the web away from a potential source of wetting. Thus, using a needle punch to pre-process a fibrous web prior to stitchbonding has the effect of reducing the overall moisture absorption capacity of the web. Such reduced moisture retention capacity has been a barrier to more widespread use of reusable diapers, as they continue to underperform in comparison to disposables.
Another problem associated with prior art reusable diapers is the loss of integrity after repeated washings. This can be caused by shrinking, change of shape, or degradation in the quality of the absorbent mat.
There is therefore a need in the art for a reusable and washable diaper or mat composition which provides improved fluid absorbency and fluid dispersion characteristics over the prior art and comparable to those of disposable diapers. Moreover, there is a further need for a reusable and washable diaper which can maintain its size, shape and form after repeated washings.